The embodiments described herein relate generally to a mass spectrometer (MS) systems that employ molecular ionization and, more particularly, to MS systems that separate ionized molecules from neutral molecules such that the two groups of molecules arrive at a detector at different times.
Most known mass spectrometer (MS) systems are typically used to detect one or more trace molecules of materials of interest from a sample. For example, a MS system may be used to detect the existence of toxic or otherwise dangerous compounds in a room. MS systems are also used to analyze drug compounds in solvents. Many known MS systems ionize trace molecules from a gas sample and then deflect the ionized molecules into a detector. The detector may detect the mass of the ionized molecule by measuring the time required for the molecule to travel across a chamber or by other means. The identity of the molecule can then be determined from the mass and the charge on the ionized molecules, i.e., the mass-to-charge ratio (m/z) is used to identify the chemical constituency of the ionized molecules.
In most known MS systems, the ratio of the number of neutral molecules to ionized molecules is on the order of magnitude of 1010 to 1. The transmission of neutral molecules to the detector increases the level of interference detections, i.e., “noise” processed by the detector, thereby inhibiting operation of the MS system. Therefore, many known MS systems include mechanisms to decrease the number of neutral molecules that reach the detector. However, most of these known mechanisms increase the size, weight, complexity, and cost of the associated MS systems.
For example, since most known MS systems operate at less than atmospheric pressure, vacuum pumps are used to maintain the low pressures in the MS systems. Exceeding low pressure parameters may decrease the service life of the associated MS systems. Transmission of the ionized molecules to the detector includes generating a pressure wave that includes the ionized molecules as well as a large number of neutral molecules. The vacuum pumps are used to remove at least a portion of the neutral molecules in the pressure wave while maintaining the pressure within the MS system below the pressure parameters. However, to remove a sufficient number of neutral molecules, the vacuum pumps needed are large, thereby decreasing the portability of the MS systems while increasing the size, weight, and cost. This issue is amplified in those known MS systems that include multiple vacuum chambers, each chamber with a dedicated vacuum pump, such a configuration often referred to as a differential pumping configuration.
Some known MS systems include apparatus to deflect the ionized particles away from the neutral particles. However, removal of the neutral particles from the vacuum space requires sufficiently large vacuum pumps, thereby frustrating efforts to decrease the size, weight, and cost of the MS systems. Therefore, simply decreasing the size of the vacuum pumps decreases the neutral molecules removed, thereby necessitating a decrease in the size of the sample that will be ionized and transmitted to the detector, thereby decreasing the sensitivity of the MS system with respect to the detection of the materials of interest.